Additional commandsIn SysVinit, services can define arbitrary commands. Examples would be service iptables panic, or service httpd graceful. Native systemd services do not have this ability.

Any service that defines an additional command in this way would need to define some other, service-specific, way to accomplish this task when writing a native systemd service definition.

Check the package-specific release notes for any services that may have done this.

Runlevels

runlevels are used with telinit and on the kernel command line in SystemVinit. These traditional ways of switching runlevels still work with systemd, but additionally, the following can be used instead.

SystemVinit Runlevel

Systemd Target

Notes

0

Halt the system.

1, s, single, emergency

Single user mode.

2, 4

User-defined/Site-specific runlevels. By default, identical to 3.

3

runlevel3.target, multi-user.target

Multi-user, non-graphical. Users can usually login via multiple consoles or via the network.

5

runlevel5.target, graphical.target

Multi-user, graphical. Usually has all the services of runlevel 3 plus a graphical login.